1. Field of the Invention
The present invention relates to curing catalysts for use in curing epoxy resins and the like/ and also relates to epoxy resin compositions containing the curing catalysts.
2. Description of the Related Art
Epoxy resin is an excellent thermosetting resin having well-balanced characteristics such as electrical insulating characteristic and mechanical strength. Thus, it has been widely employed in various fields including electrical insulating materials.
The epoxy resin is cured by heating; however, its curing rate is low by nature. To increase the curing rate, various types of catalysts are usually used. Conventionally used as such catalysts are dicyandiamido, BF.sub.3 complexes, imidazole derivatives and the like.
When a conventional catalyst is used in an epoxy resin composition, the cure of an epoxy resin gradually proceeds from the time of blending, even at room temperature. In other words, the reaction occurs in the epoxy resin composition as a result of mere storage, resulting in a cured epoxy resin. Therefore, the epoxy resin has a limited term of the storage and must be used within the term.
The curing reaction by using of the conventional catalysts is mediated by an ionic material. Hence, the ionic material remaining in a cured resin after the curing reaction causes a significant deterioration in the electrical insulating characteristics of the resin.